There exists an interoperability issue for OSPF over tunnel-interfaces with 5.9.x.x vs. 5.8.x.x or 6.x.x.x. By default, both sides of an OSPF adjacency tell the other side what they believe the MTU is on the interface over which they are sending packets. If one side gets a different (actually smaller) MTU than what it believes is the MTU, the adjacency is not formed. Previous to 188.8.131.52, we always used an MTU of 1500 on tunnel-interfaces. In SonicOS 5.9, a more realistic MTU (1446) was assigned to tunnel-interfaces populated in ZebOS.
Unfortunately, this breaks compatibility with the unnumbered tunnel-interface implementation on 5.8.x and 6.x.x.
The following workaround has to be configured from the CLI.
The OSPF CLI provides a command that will force OSPF to ignore MTU differences on a particular interface. In this case, it's the 5.9.x.x OSPF code that complains about the MTU since the value sent from 5.8.x and 6.x.x is 1500 - larger than the 1446 MTU for the tunnel-interface in 5.9.x.x.
On the SonicOS 5.9.x.x appliance do the following:
1. Enter Configuration mode on the SonicOS CLI. 2. Navigate to Routing, then OSPF in the CLI. 3. Show the OSPF interfaces with the "show ip ospf interface" command. You should see the tunnel-interface you want to configure in the list. 4. Enter configuration mode in the OSPF CLI with the "configure terminal" command. 5. Configure the tunnel interface with the "interface " command. 6. Disable the MTU comparison with the "ip ospf mtu-ignore" command. 7. Exit back to the non-config OSPF prompt. 8. Save the change with the "write file" command. 9. Exit out of the CLI config.
ZebOS version 7.7.0 IPIRouter 7/2009 ARS OSPF>show ip ospf interface TI2 is up, line protocol is up Internet Address 184.108.40.206/24, Area 0.0.0.0, MTU 1446 Process ID 0, Router ID 10.0.0.1, Network Type POINTOPOINT, Cost: 1 Transmit Delay is 1 sec, State Point-To-Point Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Crypt Sequence Number is 1385167419 Hello received 178 sent 178, DD received 3 sent 4 LS-Req received 1 sent 1, LS-Upd received 3 sent 3 LS-Ack received 2 sent 3, Discarded 0 ARS OSPF>configure terminal ARS OSPF(config)>interface TI2 ARS OSPF(config-if)>ip ospf mtu-ignore ARS OSPF(config-if)>exit ARS OSPF(config)>exit ARS OSPF>write file Configuration saved to OSPF ARS OSPF>exit (config-routing)# end config # end